#region Using Directives and Copyright Notice

// Copyright (c) 2006-2010, Bit Plantation (ABN 80 332 904 638)
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//     * Neither the name of the Computer Consultancy Pty Ltd nor the
//       names of its contributors may be used to endorse or promote products
//       derived from this software without specific prior written permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
// ARE DISCLAIMED. IN NO EVENT SHALL COMPUTER CONSULTANCY PTY LTD BE LIABLE 
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
// DAMAGE.

using System;
using System.Data;
using System.Data.SqlClient;

#endregion

namespace Interlace.DatabaseManagement
{
	public class DatabaseLock : IDisposable
	{
		SqlConnection _connection;
		string _name;
		bool _acquired;

		public DatabaseLock(SqlConnection connection, string name)
		{
			_connection = connection;
			_name = name;
			_acquired = false;
		}

		public bool Acquire()
		{
			return Acquire(new TimeSpan(0));
		}

		protected virtual string LockMode
		{
			get { return "Exclusive"; }
		}

		public bool Acquire(TimeSpan timeout)
		{
			if (_acquired) 
			{
				throw new InvalidOperationException("An attempt was made to lock a " +
					"DatabaseLock instance when it was already locked previously.");
			}

			using (SqlCommand command = _connection.CreateCommand())
			{
				command.CommandText = "sp_getapplock";
				command.CommandType = CommandType.StoredProcedure;

				command.Parameters.Add("@Resource", SqlDbType.VarChar);
				command.Parameters.Add("@LockMode", SqlDbType.VarChar);
				command.Parameters.Add("@LockOwner", SqlDbType.VarChar);
				command.Parameters.Add("@LockTimeout", SqlDbType.Int);

				command.Parameters.Add("@ErrorCode", SqlDbType.Int);
				command.Parameters["@ErrorCode"].Direction = ParameterDirection.ReturnValue;

				command.Parameters["@Resource"].Value = _name;
				command.Parameters["@LockMode"].Value = LockMode;
				command.Parameters["@LockOwner"].Value = "Session";
				command.Parameters["@LockTimeout"].Value = timeout.TotalMilliseconds;

				command.ExecuteNonQuery();

				if ((int)command.Parameters["@ErrorCode"].Value == -999)
				{
					throw new ArgumentException("A call to the SQL Server function " +
						"sp_getapplock failed because of a parameter validation (or other " +
						"fault) error.");
				}

				if ((int)command.Parameters["@ErrorCode"].Value >= 0)
				{
					_acquired = true;
					return true;
				}
				else
				{
					return false;
				}
			}
		}

		public void Release()
		{
			if (!_acquired) 
			{
				throw new InvalidOperationException("An attempt was made to unlock a " +
					"DatabaseLock instance when it was not locked.");
			}

			using (SqlCommand command = _connection.CreateCommand())
			{
				command.CommandText = "sp_releaseapplock";
				command.CommandType = CommandType.StoredProcedure;

				command.Parameters.Add("@Resource", SqlDbType.VarChar);
				command.Parameters.Add("@LockOwner", SqlDbType.VarChar);

				command.Parameters.Add("@ErrorCode", SqlDbType.Int);
				command.Parameters["@ErrorCode"].Direction = ParameterDirection.ReturnValue;

				command.Parameters["@Resource"].Value = _name;
				command.Parameters["@LockOwner"].Value = "Session";

				command.ExecuteNonQuery();

				if ((int)command.Parameters["@ErrorCode"].Value == -999)
				{
					throw new ArgumentException("A call to the SQL Server function " +
						"sp_releaseapplock failed because of a parameter validation (or other " +
						"fault) error.");
				}

				_acquired = false;
			}
		}

		public void Dispose()
		{	
			if (_acquired)
			{
				Release();
			}
		}
	}
}
